Catalytic process of preparing unsaturated aldehydes and acids



United States Patent 3,401,198 CATALYTIC PROCESS OF PREPARING UNSATU- RATED ALDEHYDES AND ACIDS Jamal S. Eden, Akron, Ohio, assignor to The B. F. GoodgchkCompany, New York, N.Y., a corporation of New or No Drawing. Filed Aug. 30, 1965, Ser. No. 483,862 11 Claims. (Cl. 260533) This invention relates to new and useful catalysts and to a method of preparing unsaturated aldehydes and unsaturated carboxylic acids by oxidation of unsaturated hydrocarbons at an elevated temperature, and relates more particularly to catalysts comprising a mixture of a molybdenum oxide, tellurium oxide and an alkaline earth, Group II-A, metal phosphate in a molar ratio of 100 M00 -100 TeO and 10-100 of a II-A metal phosphate and to a method of preparing acrolein and acrylic acid, or methacrolein, and methacrylic acid by passing vapors of propylene of isobutylene and an oxygen containing gas over the catalyst at a temperature of from about 325 C. to about 550 C. The catalyst can also be designated as MO10T1 10M2 20P2 20039 120 the P being in the form of a phosphate i.e. each P is attached to 3 or 4 oxygen atoms and wherein M is a Group II-A metal.

Numerous attempts have been made in the past to prepare products of higher oxidation state from hydrocarbons, especially from the normally gaseous hydrocarbons. However, all prior catalysts and procedures for oxidizing monoolefinic gaseous hydrocarbons to monoolefinically unsaturated aldehydes or monoolefinically unsaturated carboxylic acids with the same number of carbon atoms as the hydrocarbon having serious short-comings. The catalysts either have a very short active life, or they convert only a portion of the hydrocarbon to desired end groups per pass; they oxidize the hydrocarbon excessively to form high proportions of carbon monoxide or carbon dioxide or both; they are not sufliciently selective, so that the hydrocarbon molecule is attacked at both the olefinic unsaturation and at a methyl group; or the oxidation of the olefin does not proceed beyond the aldehyde stage.

It is therefore unexpected to find a catalyst having unusually long life that will convert a substantial amount, more than 50% per pass, of a gaseous monoolefin such as propylene or isobutylene to yield very high proportions of acrolein and acrylic acid or methacrolein and methacrylic acid. It is also unexpected to find a catalyst that produces a wide range of ratios of olefinic aldehyde to monoolefinically unsaturated carboxylic acid by controllable changes in reaction conditions or catalyst composition. Mol percent efficiencies of about to 65 for the aldehyde and about 21 to for the unsaturated carboxylic acid have been obtained with the catalyst and process of this invention. Usually when the efiiciency for conversion of the hydrocarbon to aldehyde is high the efiiciency for the conversion to acid is low and vice versa. This provides a great degree of flexibility in the process, so as to provide means for obtaining a product mix that may 'be needed at any particular time during commercial operation:

The reactants The essential reactants are (l) propylene or isobutylene and (2) an oxygen containing gas, which can be pure oxygen, oxygen diluted with an inert gas, oxygen enriched air or air without additional oxygen. For reasons of economy, air is the preferred oxygen containing reactant.

For the purpose of this invention the hydrocarbons which are oxidized can be defined generically by the formula H un-1 'result from the oxidation of only one methyl group on the hydrocarbon molecule while the terminal CI-I2=(|3 remains intact.

Stoichiometric ratios of oxygen to olefin for the purpose of this invention are 1.5 to 1. Slightly lower amounts of oxygen can be used at a sacrifice of yield. It is preferred, however, to use 33 to 66% excess oxygen. Larger excesses do not impair the yields of aldehydes and acids, but for practical considerations an excess much above 100% would require extremely large equipment for a given production capacity.

The addition of steam into the reactor along with the hydrocarbon and oxygen containing gas is desirable but not absolutely essential. The function of steam is not clear, but it seems to reduce the amount of carbon monoxide and dioxide in the efliuent gases.

Other diluent gases can be used. Surprisingly, saturated hydrocarbons such as propane are rather inert under the reaction conditions. Nitrogen or other known inert gases can be used as diluents if desired.

The catalyst and its preparation There are several methods for the preparation of the catalyst, which can be supported or unsupported. It is possible to dissolve each of the starting ingredients in water and combine them from the aqueous solutions or the ingredients can be dry blended. Because of the more uniform blend obtained by the solution procedure, it is preferred.

A general procedure for preparing a catalyst from water soluble ingredients is to dissolve the requisite amount of a molybdenum salt, a tellurium salt and a II-A metal salt in water. Add the requisite amount of phosphoric acid to the IIA metal salt solution. Add the tellurium salt solution to the molybdenum salt solution and then add the II-A metal salt-phosphoric acid mixture to the molybdenum-tellurium salt mixture. The catalyst is then dried and baked at 400 C. for about 16 hours.

Supported catalysts can be prepared by adding a dry support or an aqueous slurry thereof to the aqueous solution of catalyst or the aqueous catalyst ingredients can be added to the slurry of the support.

Alternatively, a slurry of the catalyst ingredients can be prepared in water, then dried and baked. For supported catalysts the aqueous slurry of the catalyst ingredients can be added to an aqueous suspension of the support or vice versa, and then dried and baked.

Another method is to blend the dry ingredients of the desired particle size and then mix them thoroughly. Thorough blending and uniform particle size is desired.

Specific examples of the solution method are now set forth.

In this procedure the ingredients are precipitated on blending.

(a) Dissolve 105.96 g. of ammonium molybdate (4H O) in 300 ml. of distilled water.

(b) Dissolve 31.922 g. TeO in ml. of concentrated HCl.

Add the tellurium salt solution to the ammonium molybdate solution. A precipitate forms.

(c) Dissolve 44.4 g. CaCl in 100 ml. of water and add 46.2 g. of H PO Add this mixture slowly to the precipitated ammonium molybdate-TeO mixture.

Dry on a steam bath and bake for 16 hours at 400 C. Thereafter, the catalyst is ground to the desired mesh size and sieved. For supported catalysts an aqueous slurry of the support can be added to the catalyst ingredients, or vice versa, prior to drying and baking.

A catalyst containing magnesium was prepared as follows:

(a) Dissolve 105.96 g. of ammonium molybdate (4H O) in 300 ml. distilled water.

(b) Dissolve 31.922 g. TeO in 75 ml. concentrated HCl and filter if necessary.

Add the tellurium salt solution to the ammonium molybdate solution. A precipitate forms.

(c) Dissolve 81.33 g. MgCl -6H O in 80 ml. of water and add 46.2 g. of 85% H PO Add this mixture slowly to the precipitated ammonium molybdate-Te mixture.

Dry on a steam bath and bake for 16 hours at 400 C. Thereafter, the catalyst is ground to the desired mesh size and sieved. For supported catalysts an aqueous slurry of the support can be added to the catalyst ingredients, or vice versa, prior to drying and baking.

A supported catalyst may be prepared by adding to (c) above 240 grams of an aqueous colloidal dispersion of microspheroidal silica in a concentration of 30-35% SiO (Ludox H.S.). The silica may also be added to one of the individual ingredients or (0) added to the silica dispersion.

Among the suitable supports are silica, silica containing materials, such as diatomaceous earth, kieselguhr, silicon carbide, clay, aluminum oxides and even carbon, although the latter tends to be consumed during the reaction.

The exact chemical structure of the catalysts made by the above procedures is not known, but catalysts with molar ratios of 100 Mo, -100 Te and 10 -100 of a calcium or magnesium phosphate can be used for oxidizing the monoolefinic hydrocarbon to aldehyde and/or carboxylic acid. The catalyst contains chemically bound oxygen so that the generic formula can be written as or magnesium or other phosphate The phosphate can be a P0,, radical, a pyrophosphate, or a polyphosphate, for example, calcium diphosphate, calcium hypophosphate, calcium metaphosphate, calcium monophosphate, calcium pyrophosphate, calcium triphosphate, magnesium phosphate, magnesium acid phosphate, magnesium pyrophosphate, barium pyrophosphate, strontium orthophosphate, beryllium phosphate and the like. The calcium and magnesium phosphates are preferred, especially as the pyrophosphates.

Preferred catalysts are ones having a ratio of 75 M00 25 TeO and 25 Ca P O or 75 M00 25 TeO and 25 Mg P O because they give high yields of desired products and the preferred support is silica, because of its low cost and good fluidizing characteristics.

Reaction conditions The reaction can be caried out in either a fixed or fluidized catalyst bed.

The reaction temperature can range from about 300 to 450 C. for the oxidation of propylene but the preferred range is from about 325 to about 425 C. Below 325 C. the conversion per pass is lower and low temperature tends to produce more aldehyde than desired. Usually, a longer contact time is needed at lower temperatures to obtain the yields of desired products obtainable at higher temperatures. Above 425 C. in the propylene oxidation some of the desired end products appear to be oxidized to carbon oxides. This is much more apparent at 450 C. For isobutylene, oxidation temperatures of 375-550 are desirable with the preferred range being 300450 C.

The molar ratio of oxygen to propylene or isobutylene should be at least 2 to 1 for good conversion and yields. Some excess oxygen, 33 to 66 mol percent is even more desirable and is preferred. There is no critical upper limit as to the amount of oxygen, but when air is used as the oxygen containing gas it becomes apparent that too great an excess will require large reactors, pumping, compressing and other auxiliary equipment for any given amount of desired end product. It is therefore best to limit the amount of air to provide a 33 to 66% excess of oxygen. This range provides the largest proportion of acid, under given reaction conditions. Also, since care is needed to avoid an explosive mixture, the limiting of air aids in that direction.

The molar ratio of steam to propylene or isobutylene can range from 0 to about 5 to 7, but best results are obtained with molar ratios of about 3 to 5 per mol of olefin and for this reason are preferred.

The contact time can vary considerably in the range of about 2 to 70 seconds. Best results are obtained in a range of about 8 to 54 seconds and this range is preferred. Longer contact times usually favor the production of acid at any given temperature.

The particle size of catalyst for fixed bed operations used is from l018 mesh. As is known, for fixed'beds, the size may be of a Wider range particle size. For fluid bed systems the catalyst size should be from 325 mesh (U.S. Sieve).

The reaction can be run at atmospheric pressure, in a partial vacuum or under induced pressure up to 50-100 p.s.i. Atmospheric pressure is preferred for fixed bed systems and a pressure of 1 to 100 p.s.i. for fluid bed reactions. Operation at a pressure which is below the dew point of the unsaturated acid at the reaction temperature is advantageous.

The data in the examples show that variations in percentages of unsaturated acids and aldehydes can be obtained with a single catalyst, using fixed ratio of reactants but changing the temperature and/or contact time. Further variation is obtainable by controlling the other variables in the reaction including the catalyst compositions within the limits set forth herein.

The examples are intended to illustrate the invention but not to limit it.

The examples A series of runs was made in a fixed bed reactor of a high silica (Vycor) glass tube 12 inches long and 30 mm. outer diameter. The reactor had three inlets, one for air, one for steam and one for propylene. Three external electrically operated heating coils were wound on the reactor. One of the coils extended along the entire length of the reactor and each of the remaining coils extended only about one half the length of the reactor.

Outlet vapors were passed through a short water cooled condenser. Uncondensed gases were passed through a gas chromotograph (Perkin-Elmer model 154D) and analyzed continuously. The liquid condensate was weighed and then analyzed for acrylic acid and acrolein in the gas chromatograph.

The reactor was filled to about of its capacity with v170 ml. of a catalyst made by the solution method described above, using a ratio of M00 33.33 TeO and 33.33 Ca P O Empirically the catalyst is and the P is present as P 0 The catalyst was not supported and had a mesh size of 10-18 (U.S. Sieve).

Steam at a temperature of ZOO-250 C. was first passed into the reactor. Then propylene and air were separately fed into the stream of water vapor. This mixture then passed through a pre-heater and entered the reactor at about ZOO-250 C. The reactor was pre-heated to about 285 C. before the gas feed was begun.

The ratio of reactants was about 2.955 mols of oxygen and 4.36 mols of steam per mol of propylene. Cold contact time was varied as indicated.

The reaction temperature was varied as the reaction proceeded.

The table below summarizes the data obtained in these 3. The method of claim 2 in which the M to P ratio runs: is 1.

Mol percent Contact Mol percent Yield on Run Temp., time, propylene propylene M01 percent No. C seconds converted converted etficiency Acr.=Acrolein.

AA=Aerylic acid.

The reactor was then filled to about 90% of its capacity 4. The method of claim 2 in which the catalyst has with 170 ml. of a catalyst made by the solution method the empirical formula Mo Te Ca P O and the described above, using a ratio of 100 M 33.33 TeO P is present as P 0 and 33.33 MggPgoq. Empirically the catalyst is 5. The method of claim 2 in which the catalyst has the em irical formula Mo Te M P O and the P 1O0 33.33 6G.6 66.6 600 is ppresent as P207 mo 866's 600 and P is present as P 0 The catalyst was not supported 6. The method of claim 2 wherein the catalyst contains, and had amesh size of 10-18 (U.S. Sieve). in molar ratios, 100 M00 10-100 Te0 and 10-100 Steam at a temperature of 200-250 C. was first passed CHgPgOq. into the reactor. Then propylene and air were separately 7. The method of claim 2 wherein the catalyst contains,

fed into the stream of water vapor. This mixture then in molar ratios, 100 M00 10-100 TeO and 10-100 passed through a pre-heater and entered the reactor at Mg P O7.

about ZOO-250 C. The reactor was pre-heated to about 8. The method of claim 2 wherein the catalyst contains,

285 C. before the gas feed was begun. in molar ratios, 100 M00 10-100 TeO and 10-100 The ratio of reactants was about 2.955 mols of oxygen Sr P O and 4.36 mols of steam per mol of propylene. Cold con- 9. A method of preparing a mixture of acrylic acid tact time was seconds. comprising passing a mixture of propylene, an oxygen The reaction temperature was varied as the reaction 30 containing gas containing from about 1.5 mols of oxygen proceeded. per mol of propylene and up to 7 mols of water vapor The table below summarizes the data obtained in these per mol of propylene through a bed of a catalyst com- I'uns: prising MO1 TC33 3M P 606o0 wherein M is a group Mol percent Yield Run Temp., M01 percent on propylene M01 percent N0. C. propylene converted efficiency converted Aer. AA Acr. AA

Aer.=Acrolein. AA=Acrylic acd. I claim: Ii-A metal and in which the P is present as P20 at a 1. A method of preparing a mixture of unsubstituted temperature of from about 350 to about 425 C. monoolefinic aldehydes and monoolefinic monoc-arboxylic 10. A method of preparing a mixture of methacrolein acids by oxidation of a methyl group of a hydrocarbon and methacrylic acid comprising passing a mixture of having the structure isobutylene and an oxygen containing gas in an amount H 50 sufficient to provide from about 1.5 to about 3 mols 0t (CHM-1 oxygen per mol of isobutylene, through a bed of a CH3C=CH2 catalyst comprising hiO1oTe 1 M2 2gP2 2 O39 120 Wherecomprising passing over a catalyst bed a mixture of gases m M 15 a group metal and m Whlch F to P Tatlo having a molar ratio of 1 mol of said monoolefinic hydro- F f M5 to 6 to 3 to 2: and Whlch each P carbon, an oxygen containing gas containing about 1.5 59 is Combmed Wlth 3 to 4 atoms Q Oxygen to 4 mols of oxygen and up to 7 mols of water vapor per The method of 9 Whlch catalyst 15 mol of said monoolefinic hydrocarbon, at a temperature MO100T33-3M66.6P66.6O60O 1n Whlch the P 18 Present a5 a of from about 300 C. to about 500 C., the said catalyst Phosphateconsisting essentially, on a molar basis, of Ref ences Cited 60 10 1 10 2-20 2-20 'as-120 UNITED STATES PATENTS wherein M is a group II-A metal and in which each P 1,882,712 10/1932 Andrussow et al. 252-437 is combined with 3 to 4 atoms of oxygen and the M to P 2,627,527 2/ 1953 Connally et a1 260--533 ratio ranges from 5M to GP to 3M to 2P. 3,192,259 10/ 1961 Fetterly et al. 260533 2. A method of preparing a mixture of acrolein and 6 acrylic acid comprising passing a mixture of propylene, FOREIGN PATENTS and an oxygen containing gas containing from about 1.5 693,142 8/1964 Canadato 4 mols of oxygen per mol of propylene over a catalyst 903,034 8/1962 Great Bfltamhaving the empirical formula OTHER REFERENCES 10 1 10 2-20 2 20 39-120 Derwent Delayed Belgian Report, No. 28, Aug. 21, wherein M is a group II-A metal and in which each P 1964, General Crgamc smtlon: P- atom is combined with 3 to 4 atoms of oxygen and the M to P ratio ranges from 5M to 6? to 3M to 2P, at a tem- HENRY JILES Pr'mary Exammer' perature of from about 350 C. to about 450 C. D. STENZEL, Assistant Examiner. 

1. A METHOD OF PREPARING A MIXTURE OF UNSUBSTITUTED MONOOLEFINIC ALDEHYDES AND MONOOLEFINIC MONOCARBOXYLIC ACIDS BY OXIDATION OF A METHYL GROUP OF A HYDROCARBON HAVING THE STRUCTURE 